ANDROID – INTERFACE AND LAYOUT

L. Grewe

Interfaces: Two Alternatives Code or XML You have two ways you can create the

interface(s) of your Application. 1. Code = write code using SDK with

classes like LinearLayout, TextView, ……

2. XML = create XML files in res/Layout (i.e. main.xml) that contain Android XML view tags like <LinearLayout> <TextView>, etc.

Lets look at this option first

Option: XML Interface

XML Interface Creation

Generally, I would say if it is possible, doing XML would be better as it means a decoupling of design from Java code.

You can have both in your system…. Lets discuss this first.

The Layout --- the interface

Layouts defined with XML located in

res/layout

The Layout-the interface res/layout/main.xml = contains layout for

interface<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:orientation="vertical"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

>

<TextView

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="@string/hello"

/>

</LinearLayout>

The above will create an interface in vertical (versus portrait) mode that fills the parent

Both in width and write and wraps and content as necessary.

XML interface

it's a tree of XML elements, Inspired by web authoring Build up UI quickly

each node is the name of a View class (example is just one View element). Create your own View ---extends Each node can have multiple attributes Look to API for details

XML interface

<TextView xmlns:android="http://schemas.android.com/apk/res/android"  android:layout_width="fill_parent"  android:layout_height="fill_parent"  android:text="@string/hello"/> xmlns:android XML namespace declaration that tells the Android tools that

you are going to refer to common attributes defined in the Android namespace. The outermost tag in every Android layout file must have this attribute.

android:layout_width This attribute defines how much of the available width on the screen this View should consume. As it's the only View so you want it to take up the entire screen, which is what a value of "fill_parent" means.android:layout_height This is just like android:layout_width, except that it refers to available screen height.

android:text This sets the text that the TextView should display. In this example, you use a string resource instead of a hard-coded string value. The hello string is defined in the res/values/strings.xml file.

Using Eclipse IDE to Visually Create XML file

Visual creation of XML file Create New->Other->Android->XML file-

Select for layout type Play with it….

drag and drop

Using Eclipse IDE to Visually Create XML file

Visual creation of XML file Create New->Other->Android->XML file-

Select for layout type Play with it….

drag and drop

Visually Creating XML interface

I dragged and dropped an EditText view and a Button. Below I show you the corresponding code.

res/layout/main2.xml

<?xml version="1.0" encoding="utf-8"?>

<AbsoluteLayout

xmlns:android="http://schemas.android.com/apk/res/android"

android:orientation="vertical"

android:layout_width="match_parent"

android:layout_height="match_parent">

<EditText android:text="@string/hello" android:id="@+id/editText1" android:inputType="textMultiLine" android:layout_width="169dp" android:layout_height="115dp" android:layout_x="11dp" android:layout_y="20dp"></EditText>

<Button android:id="@+id/button1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Button" android:layout_x="27dp" android:layout_y="146dp"></Button>

</AbsoluteLayout>

Besides drag and drop you can edit the xml file directly. Lets discuss some of the Android XML Interface related tags

XML Interface tags

Control structure of interface

Layout Tags

Layout Tags

Determines how the layout is structured. Some Tags

LinearLayout A Layout that arranges its children in a single column or a single row.

The direction of the row can be set by calling setOrientation(). You can also specify gravity, which specifies the alignment of all the child elements by calling setGravity() or specify that specific children grow to fill up any remaining space in the layout by setting the weight member of LinearLayout.LayoutParams. The default orientation is horizontal.

AbsoluteLayout A layout that lets you specify exact locations (x/y coordinates) of its

children. Absolute layouts are less flexible and harder to maintain than other types of layouts without absolute positioning.

RelativeLayout FrameLayout TableLayout

LinearLayout XML tag Visual creation of XML file XML Attributes Attribute Name Related

Method Description android:baselineAligned setBaselineAligned(boolean) When set to false, prevents the layout from aligning its children's baselines.  android:baselineAlignedChildIndex setBaselineAlignedChildIndex(int) When a linear layout is part of another layout that is baseline aligned, it can specify which of its children to baseline align to (that is, which child TextView).  android:gravity setGravity(int) Specifies how to place the content of an object, both on the x- and y-axis, within the object itself.  android:measureWithLargestChild When set to true, all children with a weight will be considered having the minimum size of the largest child.  android:orientation setOrientation(int) Should the layout be a column or a row? Use "horizontal" for a row, "vertical" for a column.  android:weightSum Defines the maximum weight sum. 

Control structure of interface, but commonly a sub-area

Related Layout Tags

ListView <ListView …..> A view that shows items in a

vertically scrolling list.Attributes android:divider Drawable or color to draw between list

items.  android:dividerHeight Height of the divider.  android:entries Reference to an array resource that

will populate the ListView.  android:footerDividersEnabled When set to false, the

ListView will not draw the divider before each footer view. 

android:headerDividersEnabled When set to false, the ListView will not draw the divider after each header

view. 

Gallery <Gallery ….>

A view that shows items in a center-locked, horizontally scrolling list.

The default values for the Gallery assume you will be using Theme_galleryItemBackground as the background for each View given to the Gallery from the Adapter. If you are not doing this, you may need to adjust some Gallery properties, such as the spacing.

Attributes android:animationDuration setAnimationDuration(int) Sets how

long a transition animation should run (in milliseconds) when layout has changed. 

android:gravity setGravity(int) Specifies how to place the content of an object, both on the x- and y-axis, within the object itself. 

android:spacing setSpacing(int)   android:unselectedAlpha setUnselectedAlpha(float) Sets the alpha

on the items that are not selected. 

Code—setting up Gallery

@Overridepublic void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.main);

    Gallery gallery = (Gallery) findViewById(R.id.gallery);    gallery.setAdapter(new ImageAdapter(this));

    gallery.setOnItemClickListener(new OnItemClickListener() {        public void onItemClick(AdapterView parent, View v, int position, long id) {            Toast.makeText(HelloGallery.this, "" + position, Toast.LENGTH_SHORT).show();        }    });}

Making the elements of your GUI

Views and ViewGroups

Views and ViewGroups An Activity can contain views and

ViewGroups.

android.view.View.* = base class for all Views. example sub-classes include: TextView, ImageView, etc.

android.view.ViewGroup = Layout for views it contains, subclasses include android.widget.LinearLayout android.widget.AbsoluteLayout android.widget.TableLayout android.widget.RelativeLayout android.widget.FrameLayout android.widget.ScrollLayout

LinearLayout (<LinearLayout> or android.widget.LinearLayout) arranges by single column or row.

child views can be arranged vertically or horizontally. <?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:orientation="vertical" >

<Text View

android:layout_width=“fill_parent”android:layout_height=“wrap_content”android:text=“@string/hello”/>

</LinearLayout>

Linear Layout Example

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent“ android:orientation="vertical" >

<Button android:id="@+id/btn_webbrowser" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Web Browser“ android:onClick="onClickWebBrowser" />

<Button android:id="@+id/btn_makecalls" android:layout_width="fill_parent" android:layout_height="wrap_content“ android:text="Make Calls" android:onClick="onClickMakeCalls" />

<Button android:id="@+id/btn_showMap" android:layout_width="fill_parent" android:layout_height="wrap_content“ android:text="Show Map" android:onClick="onClickShowMap" />

<Button android:id="@+id/btn_launchMyBrowser" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Launch My Browser" android:onClick="onClickLaunchMyBrowser" />

</LinearLayout>

LinearLayout attributes

You can set either in XML or with set*() methods.

i.e. Xml android:orientation=“vertical”

code (ll is LinearLayout instance) ll.setOrientation(VERTICAL);

Each View or ViewGroup can have its own set of attributes…but, some are very common

Attribute Description

layout_width specifies width of View or ViewGroup

layout_height specifies height

layout_marginTop extra space on top

layout_marginBottom extra space on bottom side

layout_marginLeft extra space on left side

layout_marginRight extra space on right side

layout_gravity how child views are positioned

layout_weight how much extra space in layout should be allocated to View (only when in LinearLayout or TableView)

layout_x x-coordinate

layout_y y-coordinate